Top 20 NuGet app.config Packages

Allows for configuration based XML transformations at build time.

AutoConfig is an automagical, convention-based, customisable, extensible library for mapping configuration files to POCO C# objects/interfaces with the absolute minimum of code.

Allows for configuration based XML and JSON transformations at build time.

Cross platform Xamarin AppSettings reader

Loads application settings into your own custom data class

This T4 template that generates a static class to access your app.config and web.config settings.

Strong typed application configuration.

Simple library for reading and validating appsettings with ease.

Add-on for Mash.AppSettings to override with dev-specific settings

A simple tool to allow you to quickly pull an application setting from your web or console app, while specifying its return type.

Helpers for testing code that uses ConfigurationManager.AppSettings

Generic framework helper for profiles using a database.

Utilities for accessing server-side Sql Reporting Reports from Web sites.

Library which allows the capability to redirect your configuration sections to another source.

Makes it easy to load a strongly-typed object (or IList of objects) from a custom web.config or app.config file section without having to write a custom IConfigurationSectionHandler implementation.

Helpers to perform .config file XML transformations, and to test the resulting transformed XML (or actually any XML, whether it's .config format or not).

Makes it easy to load a strongly-typed object (or IList of objects) from a custom web.config or app.config file section without having to write a custom IConfigurationSectionHandler implementation.

strong.config provides an automatically-generated, strongly-typed facade for accessing application configuration settings.

The Config Helper Pro Library has the ability to manage all your .NET configuration needs. Read/write to the registry, application/web config, and INI files with a single line of code. Everything is 100% managed code.

ConfigZilla is a solution for applying transformations to *.config files across an entire solution in a quick and DRY-ish manner. It also provides a GUI for easy encrypting and decrypting of config files.